Tumor progression locus 2 ablation suppressed hepatocellular carcinoma development by inhibiting hepatic inflammation and steatosis in mice

Abstract

Background: Tumor progression locus 2 (TPL2), a serine-threonine kinase, functions as a critical regulator of inflammatory pathways and mediates oncogenic events. The potential role of Tpl2 in nonalcoholic fatty liver disease (NAFLD) associated hepatocellular carcinoma (HCC) development remains unknown.

Methods: Both wild-type and Tpl2 knockout male mice were initiated by a hepatic carcinogen (diethylnitrosamine, i.p. with a single dose of 25 mg.kg(-1))at 2 weeks of age, and then were given the high carbohydrate diet feeding to induce hepatic steatosis, inflammation, adenoma and HCC for 24 weeks.

Results: Tpl2 knockout mice had significantly lower incidences of liver tumor and developed hepatocellular adenoma only, which is contrast to wild-type mice where they all developed HCC. Tpl2 knockout mice had significantly down-regulated phosphorylation of JNK and ERK, and levels of mRNA expression of pro-inflammatory cytokines (Il-1β, Il-18, Mcp-1 and Nalp3), which correlated with the reduced incidence and number of hepatic inflammatory foci. Furthermore, Tpl2 ablation resulted in decreased hepatic steatosis and expression of de novo lipogenesis related markers (ACC, SCD1, SREBP1C and AKT phosphorylation), as well as reduction of endoplasmic reticulum stress biomarkers PERK and eIF-2a.

Conclusion: The study revealed for the first time that Tpl2 plays a significant role in promoting HCC development by its pro-inflammatory effect, which suggested that Tpl2 could be a molecular target for HCC prevention.

Fig. 1

Representative pathologic lesions in livers. Hepatic lesions were assessed by H&E staining. Upper panel: Normal (Left); Steatosis and inflammatory foci (Right); Middle Panel: Hepatocellular adenoma (low magnification at x 25 and x100); Lower panel: HCC (low magnification at x25 and x200)

Fig. 2

Effect of Tpl2 ablation on hepatic mRNA expression of genes related to inflammation (a) and protein phosphorylations of JNK1/2 and ERK1/2 (b). a mRNA expression of genes related to inflammatory and macrophage markers in liver tissue in mice were detected by RT-PCR analysis. Values are expressed as mean ± standard error of the mean (SEM). Actin was used as the control. b Proteins expression of JNK1/2 and ERK1/2 from liver tissue of Tpl2 knockout or wild-type mice were detected by western blotting analysis. Values are mean ± standard error of the mean (SEM). *Comparing with Tpl2 wild type group. Insets: Representative pictures of western blotting analysis

Fig. 3

Effect of Tpl2 ablation on hepatic protein expressions related to lipid metabolism (a) and AKT phosphorylation (b). Proteins expression related to lipogenesis (a) and AKT phosphorylation (b) from liver tissue were determined utilizing Western blotting analysis. Data are presented as mean ± standard error of the mean (SEM). Actin was used as the control. *Comparing with Tpl2 wild type group. Insets: Representative pictures of western blotting analysis

Fig. 4

Effect of Tpl2 ablation on hepatic ER stress biomarkers. Proteins expression related to ER stress were examined by western blotting analysis. Values are mean ± standard error of the mean (SEM). Actin was used as the control. *Comparing with Tpl2 wild type group. Insets: Representative pictures of western blotting analysis